They were soon on their way, Frank stepping bravely along, and declaring that the motion and the morning air had driven out whatever megrims the euphorbia water might have left behind. They soon came into a different character of country from that which they had recently been traversing. Hitherto they had been moving to and fro on the skirts of the great Kalahari; they were now about to pass through its central solitudes. As they advanced, the groups of trees and shrubs grew scantier, and at length almost wholly disappeared. Interminable flats of sand, varied only by heaps of stone scattered about in the wildest disorder, succeeded each other as far as the eye could reach. For miles together there was no sign of animal or vegetable life--not the cry of an insect, not the track of a beast, not the pinion of a bird. The red light of daybreak, the hot and loaded vapours of noontide, the gorgeous hues of sunset, the moon and stars hanging like globes of fire in the dark purple of the sky, succeeded each other with wearying monotony. There was no difference between day and day. They depended for their subsistence almost entirely on the roots, which De Walden knew where to search for, and which relieved the parched lips and burning throat as nothing else could have done. Their resting-place at mid-day, and at night alike, was either the shadow cast by some huge stone, or a natural hollow in its side, or more rarely a patch of scrub and grass, growing round some spring, either visible or underground. The cool sunset breeze every evening restored something of vigour to their exhausted frames, and enabled them to toil onward for another, and yet another, day. After nearly three weeks of this travel, they found the landscape begin once more to change. The kameel-doorn and the euphorbia again made their appearance, at first in a few comparatively shaded spots; then the aloe and the mimosa began to mingle with them; and in the course of a day's journey afterwards, birds chirped among the boughs, the secretary was seen stalking over the plain, and the frequent spoor of wild animals showed that they had again reached the world of living beings. Their guide now told them that they were within two days' journey or so of the Gariep; which he proposed to pass at some point immediately below one of the great cataracts. The river at this spot ran always, he said, with a rapidity which rendered it almost impossible to ford; but at the times when it was at the lowest, after long drought, as was the case now, it might be crossed by climbing along trunks of trees which had been lodged among the rocks and left there by the subsiding waters of a flood. This required nothing of the traveller beyond a steady foot and a cool head. Where there were several to help one another, the risk was reduced almost to zero.